Help with CDM-T lighting

[Part Timer]

I've tried to experiment with a Philips 70W CDM-TD (830) to replicate the sort of light I would get from a 500W (ish) tungsten halogen in the same fitting (£3.50 from Toolstation). I understand the need for a ballast, so I got a Philips HID PrimaVision Electronic Gear HID-PV C 70 /S CDM and wired it as per the diagram on the casing. L & N input, Earth connection, and the two output connections to the lamp. When I powered it up, the ballast just buzzed and the lamp didn't light at all. Is my lamp (or ballast) DOA, or am I missing something obvious like the type of cable necessary. (Have experimentally been using flex from an IEC cable, small pieces of twin and earth to the ballast connections, and choc blocks). I am aware of the voltage dangers, UV, etc before anyone asks. Purely DIY for personal use so no part P responses please!

Happy Christmas everyone!

James

[John Rumm]

Cable ought not make any difference, we are not talking high powers here, although beware the breakdown voltage of what you use for the lamp connections - you don't want something that looks like a short at 4kV

[Dave Plowman (News)]

'Ballast' tends to get used as a generic for the control gear required for any type of lamp that needs one. Regardless of how it actually works.

The ballast you're probably thinking of in older fluorescent fittings was more correctly called a choke, if you're being pedantic.

[Andrew Gabriel]

Long cable between ballast and lamp will attenuate the starting pulse.

Although the 70W TD metal halide is same size and connectors as a 500W linear halogen, they normally use different, high voltage, lampholders, because of the starting pulse. To be honest, I'd be surprised if a regular lampholder broke down at 5kV, but that's worth considering. Also, check the connection wires to it are not pressing against any sharp metalwork. If you have any PTFE sleeving, you should thread that over the connection wires.

Note that a 70W metal halide won't come close to light output of a

500W halogen - they're nowhere near that efficient. Probably more like 200-250W. The 150W metal halide is nearer to 500W halogen, but the lamp caps are completely different.

The other things to beware of when retrofitting metal halide lamps into other fittings:

They can explode, so the fitting needs to safely contain the red-hot exploding glass/quartz.

As you mentioned, they give off UV. Mostly the glass envelope blocks the harmful UV from a health perspective (unless you go to very high colour temperatures), but enough UV will come out to fade colours of things the lamp is lighting. Special glass covers are used to stop this.

The reflector must not focus the heat from the lamp back onto the lamp; that rapidly kills the lamp. This is often achieved by using a dimpled reflector to generate scattered reflection. If you use a plain reflector, then you have to make sure the lamp isn't positioned where light is focussed back onto it. This is particularly true where the fitting was used as a halogen, where reflecting the light/heat back onto the lamp is desirable as it increases the efficiency or a halogen.